Some oil and gas wells are completed in unconsolidated formations that contain loose fines and sand. When fluids are produced from these wells, the loose fines and sand can migrate with the produced fluids and can damage equipment, such electric submersible pumps (ESP) and other systems. For this reason, completions can require screens for sand control.
Horizontal wells that require sand control are typically open hole completions. In the past, stand-alone sand screens have been used predominately in these horizontal open holes. However, operators have also been using gravel packing in these horizontal open holes to deal with sand control issues. The gravel is a specially sized particulate material, such as graded sand or proppant, which is packed around the sand screen in the annulus of the borehole. During production, the gravel acts as a filter to keep any fines and sand of the formation from migrating with produced fluids.
A prior art gravel pack assembly 20 illustrated in FIG. 1A extends from a packer 14 downhole from casing 12 in a borehole 10, which is a horizontal open hole. To control sand, operators attempt to fill the annulus between the assembly 20 and the borehole 10 with gravel (particulate material) by pumping slurry of fluid and gravel into the borehole 10 to pack the annulus. For the horizontal open borehole 10, operators can use an alpha-beta wave (or water packing) technique to pack the annulus. This technique uses a low-viscosity fluid, such as completion brine, to carry the gravel. The assembly 20 in FIG. 1A represents such an alpha-beta type.
Initially, operators position a wash pipe 40 into a screen 25 and pump the slurry of fluid and gravel down an inner string 45. The slurry passes through a port 32 in a crossover tool 30 and into the annulus between the screen 25 and the borehole 10. As shown, the crossover tool 30 positions immediately downhole from the gravel pack packer 14 and uphole from the screen 25. The crossover port 32 diverts the flow of the slurry from the inner string 45 to the annulus downhole from the packer 14. At the same time, another crossover port 34 diverts the flow of returns from the wash pipe 40 to the casing's annulus uphole from the packer 14.
As the operation commences, the slurry moves out the crossover port 32 and into the annulus. The carrying fluid in the slurry then leaks off through the formation and/or through the screen 25. However, the screen 25 prevents the gravel in the slurry from flowing into the screen 25. The fluids passing alone through the screen 25 can then return through the crossover port 34 and into the annulus above the packer 14.
As the fluid leaks off, the gravel drops out of the slurry and first packs along the low side of the borehole's annulus. The gravel collects in stages 16a, 16b, etc., which progress from the heel to the toe in what is termed an alpha wave. Because the borehole 10 is horizontal, gravitational forces dominate the formation of the alpha wave, and the gravel settles along the low side at an equilibrium height along the screen 25.
When the alpha wave of the gravel pack operation is done, the gravel then begins to collect in stages (not shown) of a beta wave. This forms along the upper side of the screen 25 starting from the toe and progressing to the heel of the screen 25. Again, the fluid carrying the gravel can pass through the screen 25 and up the wash pipe 40. To complete the beta wave, the gravel pack operation must have enough fluid velocity to maintain turbulent flow and move the gravel along the topside of the annulus. To recirculate after this point, operators have to mechanically reconfigure the crossover tool 30 to be able to washdown the pipe 40.
Although the alpha-beta technique can be economical due to the low-viscosity carrier fluid and regular types of screens that can be used, some situations may require a viscous fluid packing technique that uses an alternate path. In this technique, shunts disposed on the screen divert pumped packing slurry along the outside of the screen. FIG. 1B shows an example assembly 20 having shunts 50 and 52 (only two of which are shown). Typically, the shunts 50/52 for transport and packing are attached eccentrically to the screen 25. The transport shunts 50 feed the packing shunts 52 with slurry, and the slurry exits from nozzles 54 on the packing shunts 52. By using the shunts 50/52 to transport and pack the slurry, the gravel packing operation can avoid areas of high leak off in the borehole 10 that would tend to cause bridges to form and impair the gravel packing.
Prior art gravel pack assemblies 20 for both techniques of FIGS. 1A-1B have a number of challenges and difficulties. During a gravel pack operation in a horizontal well, for example, the crossover ports 32/34 may have to be re-configured several times. During a frac pack operation, the slurry pumped at high pressure and flow rate can sometimes dehydrate within the assembly's crossover tool 30 and associated sliding sleeve (not shown). If severe, settled sand or dehydrated slurry can stick to service tools and can even junk the well. Additionally, the crossover tool 30 is subject to erosion during frac and gravel pack operations, and the crossover tool 30 can stick in the packer 14, which can create extremely difficult fishing jobs.
To deal with gravel packing in some openhole wells, a Reverse-Port Uphill Openhole Gravel Pack system has been developed as described in SPE 122765, entitled “World's First Reverse-Port Uphill Openhole Gravel Pack with Swellable Packers” (Jensen et al. 2009). This system allows an uphill openhole to be gravel packed using a port disposed toward the toe of the hole.
Today when wells are drilled into reservoirs that are intended to be completed with an open hole gravel pack such as described above, the well is drilled to the top of the reservoir, and a liner is then set and cemented in place before drilling proceeds further into the reservoir. After the liner is run and cemented, then drilling operations can resume into the intended zone. Completing these operations in separate steps and separate pipe trips into the well adds cost and time to the overall well construction operation.
Rather than performing the cementing and gravel pack in separate steps, it would be desirable to perform these in the same run downhole. One way to do this is to run a gravel pack system downhole after drilling the hole. With the gravel pack system installed, sand slurry can be pumped through a crossover tool from the top of the targeted zone to the bottom to pack the annulus around a screen with sand. The crossover tool could then be raised past the open hole packer so that the crossover tool aligns with cementing ports. Operators can then pump cement downhole to cement the liner above the open hole packer. This requires circulating through a complicated cross-over tool.
Unfortunately, the wash pipe used for the gravel pack operation will still extend through the screen during the cementing operation. If tools are out of position, cement could be pumped into the screen, effectively ruining the operation. In addition, the cement would be pumped immediately after the gravel pack operation. Therefore, if any acidizing operation is to be subsequently performed, it would have to be through pipe that would likely have residual cement, which could damage the formation.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.